| Summary: | Author Posting. © Nature Publishing Group, 2008. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature Geoscience 1 (2008): 620-624, doi:10.1038/ngeo285. The early Holocene deglaciation of the Laurentide Ice Sheet (LIS) is the most recent and best constrained disappearance of a large Northern Hemisphere ice sheet. Its demise is a natural experiment for assessing rates of ice sheet decay and attendant contributions to sea level rise. Here we demonstrate with terrestrial and marine records that the final LIS demise occurred in two stages of rapid melting from ~9.0- 8.5 and 7.6-6.8 kyr BP with the LIS contributing ~1.3 and 0.7 cm yr-1 to sea level rise, respectively. Simulations using a fully coupled atmosphere-ocean general circulation model suggest that increased ablation from enhanced early Holocene boreal summer insolation may have been the predominant cause of the LIS contributions to sea level rise. Although the boreal summer surface radiative forcing of early Holocene LIS retreat is twice that of projections for 2100 C.E. greenhouse gas radiative forcing, the associated summer surface air temperature increase is the same. The geologic evidence for rapid LIS retreat under a comparable forcing provides a prehistoric precedent for a possible large negative mass balance response of the Greenland Ice Sheet by the end of the coming century. This research was funded by National Science Foundation grants ATM-05-01351 & ATM-05-01241 to D.W.O. & G.A.S., start-up funds from the University of Wisconsin-Madison and a Woods Hole Oceanographic Institution Postdoctoral Scholarship to A.E.C., and the Woods Hole Oceanographic Institution's Ocean and Climate Change Institute (D.W.O. & R.E.C.).
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